This invention relates generally to electronic filters and particular to band pass filters for correcting distortion in input signals.
Band pass filters of the prior art were concerned primarily with distinguishing oscillating current signals according to their frequency but generally without a need to determine the exact end or beginning of a particular oscillating wave pulse. Where the envelope of an oscillating wave pulse may, at the beginning of its transmission, define a square wave, however, as it travels through a communication system having various inductances, capacitances and resistances distributed throughout the system, it generally is not square at the receiving end. The pulse envelope of the signal at the receiving end of the system becomes quite distorted such that the pulse envelope at the leading end of the pulse slopes upward and downward from the neutral voltage line to define sigmoid curves representing a ring-up, which meet with a similarly formed sigmoid curves at the end of the pulse which narrow down to the neutral voltage line to define a ring-down.
Where the individual oscillating current pulses are transmitted very rapidly, the ring-down portion of one pulse may be superimposed on the ring-up portion of the following pulse. The problem therefore, is one of distinguishing between individual pulses and the measurement of each individual pulse length.